1. Field of the Invention
This invention relates generally to semiconductor manufacturing and more particularly to an electromagnetic wafer stage for aligning and positioning a wafer in a microlithography system.
2. Description of Related Art
In the modern manufacture of semiconductor wafers using microlithography, it is necessary to accurately position and align semiconductor wafers on which circuit patterns are formed. As the feature size of the elements reproduced on a semiconductor wafer become ever smaller, the demands on the mechanical positioning and aligning of the wafer increase. A wafer stage used in aligning and positioning a wafer is disclosed in U.S. Pat. No. 4,952,858 entitled "Microlithographic Apparatus" issuing Aug. 28, 1990 to Daniel N. Galburt, the same inventor as the present invention. Therein disclosed is an electromagnetic alignment apparatus including a monolithic stage, a sub-stage and an isolated reference structure. Force actuators are interposed between the monolithic stage and the sub-stage for suspending and positioning the monolithic stage. Means for controlling a position of the sub-stage to follow the approximate position of the monolithic stage is also disclosed.
While the invention disclosed in U.S. Pat. No. 4,952,858 has accomplished its intended purpose, there is an ever increasing need to provide a wafer stage with better performance and more accurate and repeatable positioning. This is especially true in view of the ever decreasing feature sizes placed on the semiconductor wafers.